Convective Accelerometer

ABSTRACT

A convective accelerometer capable of measuring linear or angular acceleration, velocity, or angle of inclination is provided. The accelerometer comprises sensing elements that are sensitive to convection located inside a sealed housing containing a liquid agent. Applied external acceleration causes forced convection of the liquid agent, which produces variations in an electric current produced by the sensing elements that are proportional to the applied acceleration or angle of inclination. The accelerometer has a small size, extremely wide frequency and dynamic ranges, high sensitivity, simple design and is suitable for mass production. The device has a wide range of application, such as stabilization and control systems, homeland security, and oil exploration.

This application is a continuation of application Ser. No. 10/851,711filed May 21, 2004, the contents of which are hereby incorporated byreference in their entirety.

FIELD OF THE INVENTION

The invention relates to MEMS accelerometers, and more specifically tofluid-containing transducer-based MEMS accelerometers which measureacceleration, inclination, position and velocity by measuring the changein the electric current generated by a liquid flow under the effect ofexternal acceleration or free convection.

Accelerometers of different types have found wide application in manyfields including transportation, navigation, robotics, consumerelectronics, toys, and medical instruments, especially orthopedicdevices.

BACKGROUND

Various mechanical and electromechanical instruments are currently usedfor measuring acceleration, inclination, velocity, and motion, includingpiezoelectric and piezoresistive instruments, and force balanced,capacitive or convective accelerometers.

In accelerometers having a force feedback or servo-accelerometers theinertial mass is spring-suspended between two permanent magnets and canmove between these permanent magnets. The displacement of the mass dueto external acceleration is measured by standard electrodynamic methods.A signal of a sensor is amplified and the resulting current passesthrough a coil wound on the mass, thereby producing a rebalancing forcethat restores the inertial mass to its original position. Theaccelerometers of this type have high sensitivity and accuracy; however,they also have a high cost.

Another type of accelerometer which is capable of measuring an angularvelocity is based on the phenomenon of injection of gas into a chamberthrough a nozzle under the effect of external acceleration. The chamberhas two sensing elements in the form of wires arranged so that theinjected gas is uniformly distributed between the sensing elements inthe absence of external acceleration. In the presence of anacceleration, the gas accumulates near one of the wires, which becomescolder than the other wire. The difference in the resistance of the twosensing elements is proportional to the angular velocity. A maindisadvantage of such an accelerometer is the presence of a sprayingnozzle, which makes the instrument bulky and expensive.

Another type of accelerometer is a convective accelerometer. An exampleof a prior convective accelerometer is one that contains a heatingelement installed at the center of a housing and two temperature sensingelements arranged in the housing symmetrically with respect to theheating element. In the absence of external acceleration, a heated gascirculates symmetrically with respect to the heating element and thetemperature sensors are essentially at the same temperature so that thedifference of their readings is close to zero, thereby indicating thequiescent state. In the presence of external acceleration this symmetryis broken, and the sensing elements are at different temperatures. Therespective temperature difference is then proportional to the externalacceleration. The disadvantages of such an instrument include a lowdynamic range, low sensitivity, and high consumption of energy due tothe presence of a heating element. Such an accelerometer is alsoincapable of measuring purely rotational motion.

Thus, there is an urgent need for highly sensitive accelerometers havinga wide frequency and dynamic range, small size, low power consumption,low weight, and low cost.

SUMMARY OF THE INVENTION

The convective accelerometer according to this invention comprises asealed housing containing an installation module that has a sensingelement. The housing further comprises a liquid agent comprising anelectrolyte. The sensing element comprises electrically conductivemembers, non-limiting examples of which include metal plates with holesand a metal mesh. Conductive members are spatially separated. Separationmay be achieved by spacing the conductive members so that they are notin direct contact, or by physically separating them with a spacermaterial, such as a dielectric spacer with holes. When metal plates anddielectric spacers are used, the metal plates and dielectric spacers arearranged such that the liquid agent flows through the holes underconditions of forced convection caused by external acceleration. Itshould be noted that the combination of the housing, the liquid agent,and the sensing element (including conductive members and any spacers)is referred to herein as a molecular electronic transducer (MET). Thesignal-conditioning electronics connected to the MET via the sensingelements are used for conversion of an output electric current, whichvaries according to the convective transfer of ions to the sensingelements, thereby allowing the measurement of acceleration, velocity orinclination.

One object of the invention is to provide a convective accelerometercomprising a sealed housing comprising a liquid agent comprising anliquid electrolyte and at least one installation module secured in thehousing. The convective accelerometer further has at least one sensingelement that is sensitive to convection and that is fixed in theinstallation module and immersed in the liquid electrolyte that flowsthrough the sensing elements under conditions of forced convectioncaused by an applied external acceleration. The convective accelerometeralso has an electric circuit connected to the one or more sensingelements that amplifies and processes the output signals generated bythis system.

Another object of the invention is to provide a convective accelerometercomprising a sealed housing containing a liquid agent comprising anelectrolyte and at least one installation module secured in the housing.The installation module has one sensing element that is immersed in theliquid agent that flows through the accelerometer under conditions offorced convection caused by applied external acceleration. In someembodiments, the sensing element includes a number of punched metalplates having punched holes, as well as a number of spacers havingpunched holes, which are arranged to separate the metal plates. Inpreferred embodiments, the spacers are positioned without a gap betweenthe metal plates and are made of a dielectric material. The convectiveaccelerometer further comprises an electric circuit connected to thesystem of sensing elements that is used for amplifying and processingthe output signals generated, by this system.

The invention also provides methods for measuring angular acceleration,angular velocity or inclination that include providing a toroidalhousing containing a liquid agent and a least one sensing element havingat least one pair of conductive members separated by punched dielectricpartitions and arranged in the cross-section of the housing. The liquidagent inside the housing moves under the effect of angular acceleration,thus transferring and dragging along ions to the sensing elements, dueto forced convection. In this case, the change of current against thatin the absence of acceleration from each conductive member in thesensing element(s) is proportional to the magnitude of angularacceleration, angular velocity or inclination depending on thegeometrical characteristics of the sensing elements and dielectricplates.

Another object of the invention is to provide a method of measuringangular acceleration and/or angle of inclination comprising (1)providing an installation module that is secured in a sealed housinghaving a toroidal channel; (2) fixing at least one sensing element thatis sensitive to convection within the installation module; (3) adding tothe sealed housing a liquid agent comprising an electrolyte; (4)connecting the one or more sensing elements to an electric circuit; (5)subjecting the housing to angular acceleration by rotating it about anaxis of sensitivity of the accelerometer normal to the plane of thetoroidal channel or by inclining it through an angle relative to thevector of gravity to produce forced convection of the liquid agent; and(6) determining the value of the angular acceleration or angle ofinclination of the housing by measuring the change of the output currentgathered from the one or more sensing elements, wherein the outputcurrent is generated in the electric circuit connected to the one ormore sensing elements.

Another object of this invention is to provide a linear accelerometercomprising a sealed housing with a channel that is partially filled witha liquid agent containing an electrolyte solution. An installationmodule is secured in the sealed housing such that the installationmodule is submersed in the liquid agent. The installation modulecontains a sensing element that is sensitive to convection of the liquidagent, and is immersed in the liquid agent, such that the liquid agentflows through the sensing element under conditions of forced convectionwhen a linear acceleration applied to the convective accelerometer. Thelinear accelerometer also provides an electric circuit connected to thesensing element, wherein said electric circuit amplifies and processesoutput signals generated by said sensing element.

One object of the present invention is to provide an accelerometerhaving an extremely high sensitivity.

Another object of the invention is to provide an accelerometer with awide frequency range and dynamic range with a simultaneous decrease ofthe intrinsic noise level.

Yet another object of the invention is to provide a small convectiveaccelerometer that can be mounted in very narrow places.

One object of the present invention is to provide a convectiveaccelerometer with a simple design and low cost in volume production.

An object of the invention is to provide a method of measurement ofangular acceleration, angular velocity or inclination that would allowmeasurement of these parameters with a high accuracy in a wide frequencyand dynamic range.

BRIEF DESCRIPTION OF THE DRAWINGS

The convective accelerometer and a method of measurement of angularacceleration and angle of inclination with the accelerometer are furtherexplained by way of example with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of one embodiment of the convectiveaccelerometer having a sensing element comprising four metal plates andthree spacers.

FIG. 2 is a side view of the device of FIG. 1.

FIG. 3 is a schematic diagram of one embodiment of an installationmodule.

FIG. 4 is a schematic view of the system of sensing elements (in anaxonometric view).

FIG. 5 is a schematic diagram of the arrangement of holes in oneembodiment of a dielectric spacer or a metal plate.

FIG. 6 is a side view of the device of FIG. 5.

FIG. 7 is a schematic axonometric view of one embodiment of a sensingelement having a plurality of metal plates with dielectric spacersarranged to separate them.

FIG. 8 is a schematic diagram of the gain-frequency characteristic ofthe transfer function of the accelerometer at different values of thethickness of the dielectric spacer.

FIG. 9 is a schematic diagram of an embodiment of a conductive member,wherein the conductive member is a mesh.

FIG. 10 is a schematic front sectional view of one embodiment of theaccelerometer, wherein the accelerometer comprises guard electrodes.

FIG. 11 is schematic view of the dependence of the output current fromone pair of conductive members on the voltage difference appliedthereon.

FIG. 12 is a schematic diagram of an electric circuit for temperaturecorrection of the accelerometer output voltage.

FIG. 13 is a schematic diagram of an electric circuit for frequencycorrection of the accelerometer output voltage.

FIG. 14 shows the dependence of the output current of the accelerometerin the absence of external acceleration on different concentration ofsalts of alkali metals.

FIG. 15 shows the dependence of the output current of the accelerometerin the absence of external acceleration on different concentrations ofiodine.

FIG. 16 is a schematic diagram of one embodiment of a guard electrode,wherein the electrode is made as a spiral-shaped ring.

FIG. 17 is a schematic diagram of one embodiment of a guard electrode,wherein the electrode is made as a cone-shaped spiral.

FIG. 18 shows one embodiment of the invention wherein the guardelectrodes are connected by a wire.

FIG. 19 is a schematic diagram of a sealed housing comprising a toroidalchannel, wherein the toroidal channel is made in such a way thatexternal and internal generating shapes are eccentric, with the degreeof separation of their centers denoted as e.

FIG. 20 is a schematic diagram of a toroidal channel with a mouthpieceinstalled therein.

FIG. 21 is a schematic diagram of a toroidal channel accommodating apair of installation modules disposed diametrically opposite to eachother, each module comprising a sensing element having two conductivemembers.

FIG. 22 is a schematic diagram of a toroidal channel with installationmodules having sensing elements with two pairs of conductive members.

FIG. 23 is a schematic diagram of a toroidal channel with an even numberof installation modules and the corresponding sensing elements.

FIG. 24 shows a linear accelerometer according to the invention.

FIG. 25 shows calibration data for an angular accelerometer according tothis invention.

FIG. 26 shows the signature of a walking person in a through-walldetection experiment. The data have been recorded with a 24-bitdigitizer at 320 sps (i.e., samplings per second.)

FIG. 27. shows heartbeat and respiration signals of a person recorded bythe rotational accelerometer from about two meter distance (24-bitdigitizer at 40 sps). The distance of such remote recording can beincreased up to 6 meters by improving parameters of the rotationalaccelerometer.

FIG. 28 shows the spectrum of the scan presented in FIG. 27.

FIG. 29 shows the spectrum recorded by CB-10, a low cost geophone. Notethat the geophone did not detect the low-frequency signals produced bythe underground equipment.

FIG. 30 shows the X-component spectrum recorded by a CME 4011 broadbandseismometer of the translational motions of the drilling equipment

FIG. 31 shows the Y-component spectrum recorded by a CME 4011 broadbandseismometer of the translational motions of the drilling equipment. Thepeak at 1.1 Hz corresponds to translational movement.

FIG. 32 shows the Z-component spectrum recorded by a CME 4011 broadbandseismometer of the translational motions of the drilling equipment. Thepeak at 1.1 Hz corresponds to translational movement.

FIG. 33 is a schematic of a molecular-electronic rotational sensor.

FIG. 34 shows a photo of a 3-component MET rotational sensor(dimensions: 100×100×100 mm³).

FIG. 35 shows an X-component spectrum recorded by a rotationalaccelerometer according to the invention.

FIG. 36 shows an Y-component spectrum recorded by a rotationalaccelerometer according to the invention.

FIG. 37 shows an Z-component spectrum recorded by a rotationalaccelerometer according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 and 2 show an embodiment of a convective accelerometer accordingto this invention that comprises a sealed housing 1, a liquid agent 2comprising an electrolyte contained in the sealed housing 1, and aninstallation module 3 (FIGS. 1, 3), in which sensing element 4 (FIG. 1)is rigidly secured.

The accelerometer may contain one or more installation modules 3 (FIG.3), each having (FIGS. 1, 4) a sensing element 4 that is sensitive toconvection. The sensing element 4 (FIG. 1) may comprise conductivemembers 5, such as, for example, two pairs 100, 200 of metal platesseparated by dielectric spacers 6. The metal plates and spacers arearranged in alternating layers and aligned so that the holes of themetal plates and the spacers coincide to allow flow of a liquid agent(e.g., one containing an electrolyte) through the holes, as shown inFIG. 4. Note that, for the sake of simplicity, FIG. 4 only shows twoconductive members 5 (shown here as metal plates) and one spacer 6,which have only one hole 7 for a free flow of the liquid agent 2 throughthe sensing element 4 as a result of applied external acceleration.However, this invention contemplates sensing elements with metal platesand dielectric spacers that have a plurality of holes. For example, theconductive members 5 can be metal plates having output contacts 8, 9,10, and 11 (see FIG. 2) and dielectric spacers 6 can be punched as shownin FIGS. 5, 6, and 7. In certain embodiments, the holes are the samesize and shape and are arranged in a regular grid pattern. Thedielectric spacers 6 are inserted between the conductive members 5 toprevent possible electric short circuits between them. However, incertain embodiments, the dielectric spacers are also used to causelaminar flow of liquid agent 2 through the sensing element 4. Thethickness of the spacer 6 also affects the frequency range of themeasurement, as set forth below. The diameter d and the number of holes7 in the spacer 6, in turn, determine the accelerometer sensitivity andhave an effect on the frequency dependence of the accelerometer transferfunction in the full frequency operating range. With an increase of thenumber of holes 7 and an increase of their diameter d the hydrodynamicimpedance of the spacer 6 decreases in inverse proportion to the numberof holes 7 and the fourth power of their diameter d. Thus, by varyingthe number and diameter of the holes, the transfer function of theaccelerometer can be varied. More specifically, the high cutofffrequency of the transfer function is proportional to the hydrodynamicimpedance, such that the frequency range increases with increasinghydrodynamic impedance. With this in mind, a useful number of holes 7 isfour or more for dielectric spacers 6 that are square, with a sidedimension of 1.5×1.5 mm. Moreover, a useful range of hole diameter isbetween about 1 and about 300 microns, and preferably between about 20to about 200 microns.

The material of the spacers 6 should be resistant to corrosion by theliquid agent 2, and should have a thermal expansion coefficient that iscompatible with the other components of sensing element 4 so as to avoiddamage as the result of temperature variations. Many different materialsmay be used, with suitable materials including, for example, oxides orfluorides of elements of the fourth group of the Periodic Table,forsterite, quartz, and glass. A useful range of spacer thickness isfrom about 0.5 to about 150 microns.

The shape of the holes 7 in metal plates 5 and dielectric spacers 6 isnot particularly limited, and may be in any shape. Geometrical shapessuch as, for example, squares, rectangles, circles and/or ovals are usedin some embodiments. However, because, the intensity of the electriccurrent passing through the conductive members of sensing element 4 isdirectly proportional to the area of the conductive member in contactwith the liquid agent 2, in a particularly preferred embodiment, theholes 7 are circular apertures with “rays” extending radially (i.e.,“star-shaped”). Various types of holes may be made in the conductivemembers and dielectric spacers by physical or chemical methods,non-limiting examples of which include stamping, laser drilling,chemical etching, and electrochemical methods.

It should be noted that the sensing element 4 may comprise a number ofconductive members 5 in the form of metal plates and a set of dielectricspacers 6 located between these metal plates 5 as shown in FIG. 7.

The number of installation modules 3 and the corresponding sensingelements 4 chosen for a particular accelerometer depends on the requireddynamic range of accelerations to be measured, the required degree oflinearity, the frequency range, and the level of intrinsic noise.Generally, increasing the number of installation modules and sensingelements leads to increased dynamic range, linearity, frequency range,and decreased intrinsic noise. When the conductive members are in theform of metal plates, it is useful to install from four to eight suchplates and three to seven spacers made of a dielectric material.Preferably, the plates and spacers are installed substantially parallelto each other, and substantially perpendicular to the local flowdirection of the liquid agent 2.

The distance between conductive members 5 affects the frequencydependence of the transfer function of the claimed accelerometer:generally, the wider the required frequency range of measurement ofaccelerations, the closer to each other the conductive members should beinstalled.

FIG. 8 illustrates data for the amplitude-frequency characteristics ofthe accelerometer when distances between conductive members are varied.The curves 12,13, and 14 correspond to a distance between the conductivemembers equal to 100, 40 and 10 microns respectively. FIG. 8 shows thatit is possible to vary the transfer functions of the accelerometer fordifferent practical applications by varying the distance between theconductive members. For an accelerometer which has an upper cut-off ofthe frequency range between several kHz up to tens of kHz (e.g., about 1kHz to about 20 kHz), the distance between the conductive members ispreferably from about 1 to about 10 microns. Accordingly, whendielectric spacers are used to separate the conductive members, thedielectric spacers should preferably be about 1 to about 10 micronsthick for this frequency range.

The conductive members 5 for some embodiments of the claimedaccelerometer can be made as a mesh comprising a plurality of wires, asshown in FIG. 9. To provide a high strength mesh, the mesh can be madeas a twill weave, and the output contacts can be connected to the meshvia lamellas 15 by electrically welding the flat output wire to themesh. For example, when the conductive element 5 is a mesh with a squareshape and a side dimension of 1.5 mm, the thickness of the mesh is inthe range of about 50 to about 90 microns, and the mesh may comprise awire with a diameter from about 25 to about 45 microns. Generallyspeaking, wires having a diameter of about 10 to about 90 microns areuseful for constructing a mesh for the convective accelerometer of thisinvention. Metals of the platinum group (Group 10) are suitablematerials for manufacture of the mesh. However, other noble metals andtheir alloys, or other corrosion-resistant conductors can also be usedfor manufacture of the conductive elements. The mesh may be fabricatedby electrically welding wires together, preferably such that the spacebetween parallel wires is about 20 to about 90 microns.

The output contacts 8, 9, 10, and 11 can be made, for example, from awire with a diameter of about 20 to about 100 microns. In preferredembodiments, the output contacts have similar thermal expansioncoefficients as that of the wire mesh and the material that is used tomake the installation module 3 and sealed housing 1.

The following provides a description of preferred ways to optimize andto operate the convective accelerometer.

The performance of the convective accelerometer according to theinvention includes three primary characteristics: noise level, dynamicrange, and frequency range. These primary characteristics may beadjusted by varying certain physical attributes (e.g., hole size, spacerthickness) of the convective accelerometer, as described below. Itshould be noted that, in some cases, varying a certain physicalattribute improves one of the primary characteristics, but degradesanother. Nevertheless, one of ordinary skill in the art would recognizethat, by routine experimentation, it is possible to arrive at a givenperformance requirement by appropriately adjusting the differentphysical attributes of the convective accelerometer of this invention.

For example, to reduce the noise level, the hydrodynamic impedanceshould be decreased and the size of the sensing element and the contactarea of conductive members with liquid agent should be increased. Thehydrodynamic impedance may be decreased by increasing the number ofholes and/or their diameters in the spacers and conductive members;increasing the space between parallel wires when a mesh-type conductivemember is used; and/or decreasing the spacer thickness, the conductivemember thickness, or both. The contact area of the conductive memberswith the liquid agent may be increased using thick conductive memberswith large holes; increasing the number of holes; selecting wires with alarger diameter and/or using rolled wires when a mesh-type conductivemember is used; and/or selecting a hole shape that has a large perimeter(e.g., a star-shape).

While the noise level of the convective accelerometer reduces bydecreasing hydrodynamic impedance, the dynamic range and linearityincrease with increasing hydrodynamic impedance. The hydrodynamicimpedance may be increased by installing mouthpieces as describedherein; and/or selecting internal and external generating shapes thatincrease the hydrodynamic impedance, as described herein.

The frequency range of the convective accelerometer can be increased bydecreasing the thickness of the spacers, and/or using smaller-diameterholes, in addition to the methods described in the previous paragraph.

As an example, when a convective accelerometer with one installationmodule and no mouthpieces has a toroidal channel with a diameter of 9mm, and a sensing element with conductive members having a thickness of30 μm, spacers with a thickness of 30 μm, and corresponding holes with adiameter of 200 μm μm, the convective accelerometer has the followingperformance characteristics: frequency range 0-1000 Hz, noise level −85dB, relative to 1 rad/sec²/√Hz, and dynamic range 138 dBs relative tothe noise in the passband 1 Hz at 1 Hz.

In the case, for example, of an angular acceleration applied to thesealed housing 1 along the arrow A (see FIG. 10), the liquid agent 2starts flowing through the conductive members 5, which are sensitive toconvection. In so doing, electric charges existing as ions of dissolvedsalts and iodine (e.g., from the dissolution of metallic iodine) arebrought to one of the conductive members 5 and are withdrawn from aneighboring conductive member, thereby generating in sensing element 4an electric current whose value is proportional to the appliedacceleration. For further amplification and processing of the electricalsignals gathered from these conductive members 5, the conductive members5 are connected (FIG. 2) to an electrical circuit 16 by means ofterminals 8, 9, 10, and 11 (FIG. 2). This circuit is schematically shownin FIG. 10.

The electrical circuit comprises an operational amplifier 17 used fortransforming the electric current gathered from the conductive member 5into a voltage. In so doing, the resistance 18 in the feedback circuitof the operational amplifier 17 determines the total amplificationfactor of the output signal gathered from conductive members 5. Theelectric circuit also includes an adder 19, which is used fordifferential connection of two pairs 100, 200 of conductive members 5.In this case, the differential current from the two pairs 100, 200 ofthe conductive members is directly proportional to the magnitude ofangular acceleration, angular velocity or inclination depending on thegeometrical characteristics of the conductive members 5 and dielectricspacers 6. The power supply 20 is used as a power supply for allelectrical circuits. The connection of the power source 20 is asfollows: the positive terminal of the source 20 is connected to theoutput contacts 8 and 11 of the conductive member 5 and the negativeterminal of the source 20 and the output contacts 9, 10 of theconductive member 5 are connected to the inputs of the operationalamplifiers 17. In the absence of an external acceleration causingconvection of the liquid agent 2 between the conductive members whichare connected to the positive and negative terminals of the power source20, a direct current J_(A) passes through the circuit. The value of thiscurrent depends on the value of the applied voltage U as shown in FIG.11. In this state, the space between the conductive members 5 connectedto the negative terminal of the power source 20 practically has nocharge carriers. When the accelerometer experiences an externalacceleration in a direction indicated by the arrow A in FIG. 10, theliquid agent 2 carries an additional charge to a first conductive member5 and carries a charge away from a second conductive member.Correspondingly, the current gathered from the first conductive member 5increases and that gathered from the second one decreases. Since thecurrent gathered from both conductive members 5 is practicallyindependent of the resistance 18 in the feedback circuit of theoperational amplifier 17, small variations of the current caused by themotion of the liquid agent 2 result in appearance of a high voltageacross the resistance 18. Thus, in sensing element 4 the signal isamplified and, depending on the value of the resistance 18, theamplification factor can be as high as 10⁷. Accordingly, the convectiveaccelerometer has an extremely high sensitivity with only a smallinertial mass in the form of liquid agent 2.

An alternative way to connect the conductive members to an electroniccircuit involves connecting the positive terminal of the power sourceand output contacts 8 and 11 of the conductive member 5 to the inputs ofthe operational amplifiers 17, and connecting output contacts 9 and 10of the conductive member 5 directly to the negative terminal of thepower source. However, the electronic noise in this case is higher athigh frequencies.

Yet another way to connect the conductive members to an electroniccircuit is to connect the positive terminal of the power source andoutput contacts 8 and 11 of the conductive member 5 to the inputs of apair of operational amplifiers, and the negative terminal of the powersource and output contacts 9 and 10 of the conductive member 5 to theinputs of another pair of operational amplifiers. The adder would havefour inputs to connect to the outputs of each operational amplifier, sothat output of the adder is a linear combination of voltages, gatheredfrom each operational amplifier. In this case, the electronic noise ishigher at high frequencies and lower at very low frequencies.

Correcting electronics can also be used for improving the temperaturestability of the accelerometer by compensating for the output voltagefluctuation due to changes of the ambient temperature, therebycompensating for changing frequency characteristics, as set forth below.Variations in the ambient temperature may affect the output signal ofthe accelerometer by changing the viscosity of liquid agent 2.Well-known methods of electronic compensation of the temperaturedependence can be used in the present invention. In one embodiment, asemiconductor thermistor 21 (FIG. 12) whose temperature coefficientcoincides with the temperature viscosity coefficient of the liquid agent2 is used to compensate for temperature variations.

The signal from the output of the adder 19 (not shown in FIG. 12) is fedthrough a resistor 22 to the input of an operational amplifier 23 whosefeedback circuit includes a thermistor 21 with adjusting resistors 24,25. When the operational amplifier 23 is inserted in the circuit shownin FIG. 12, where b, c are the inputs of the operational amplifier 23,and d, e are used for connection to the power source 20 (not shown inFIG. 12), its amplification factor varies with a change of thetemperature so as to provide a constant frequency characteristic of theaccelerometer, despite changes in the ambient temperature. Theelectronic circuitry for frequency compensation of the transfer functionof the accelerometer also can be used to extend the effective frequencyrange of the accelerometer, depending on the desired application. Forexample, the frequency range of an accelerometer with dielectric spacers6 having a thickness of 25-40 microns can be extended to a frequencyrange of an accelerometer having a spacer 6.5 to 8 microns thick byusing the frequency correction circuit.

An example of a frequency correction circuit is given in FIG. 13.

The output signal from the accelerometer V_(out) is applied to the inputof the frequency correction circuit to produce an extended passband atthe output. The frequency correction circuit comprises an operationalamplifier 26 connected as shown in the figure. The output voltage of theadder 19 (not shown in FIG. 13) is applied to the input f of theoperational amplifier 26 through a resistor 27. The input g is grounded,and h and i are used for connection of the power source 20 (not shown inFIG. 13). The resistor 28 sets the sensitivity of the accelerometer,while the correcting circuit R₂C₁ consisting of a capacitor 29 and aresistor 30 together with the resistor 27 limits the amplification ofhigh frequencies and are used for forming the required passband of theaccelerometer.

The sensitivity of the accelerometer also depends on the physical andchemical properties of the liquid agent 2 contained in the housing 1. Inpreferred embodiments, it is desirable that the liquid agent 2 has aminimum viscosity at maximum solubility. Further, the liquid agent maycomprise a salt (e.g., a salt of an alkali metal or an alkaline earthmetal) and a solute capable of acting as both a Lewis acid and a Lewisbase, such as dissolved metallic iodine. Suitable solvents for thispurpose include, for example, distilled water and organic solventscapable of dissolving organic or inorganic salts, preferably metalsalts, such as alkali salts. When dissolving the salts of alkali metals,the density of the solution increases, resulting in an increase of thesensitivity of the accelerometer. Therefore, in certain embodiments, itis desirable that the concentration of the dissolved salts is high,preferably, close to the solubility limit. Generally speaking, a usefulconcentration range for the dissolved salt is about 0.5 to about 4.0mol/liter, and preferably about 2 to about 4 mol/liter. Also, thepurities of the salt and the solute that acts as a Lewis acid/base(e.g., iodine) should be at least 98.5%, but most preferably at least99.98%. The electric current output of the accelerometer is determinedby the concentration of the dissolved metallic iodine, the ions of whichare carriers of charge that are capable to receive an electron from andto give back an electron to the conductive members 5. Thus, it is usefulto have a saturated solution of the above salts and minimumconcentration of 0.0002 N of dissolved metallic iodine. Such aconcentration of the dissolved salts provides operation of theinstrument in a wide range of negative temperatures, e.g., down to −70°C. The metallic iodine concentration may be lower, but in this case thecurrent output of the claimed accelerometer may be insufficient fornormal operation of the electric circuits, including the circuits usedfor temperature and frequency correction. A useful concentration rangefor the dissolved metallic iodine is about 0.0002 to about 0.4mol/liter, and preferably from about 2 to about 4 mol/liter. Thedissolved salts may comprise salts of metals of Group II of the periodictable which have a solubility in the fluid that is not lower than thatof salts of alkali metals. The most suitable for this purpose are, forexample, salts of barium, which, at maximum solubility, have solutiondensities that exceed the corresponding solution density of salts ofalkali metals by 1.5 times, for a given molar concentration of saltsolute.

In addition to the sensitivity, an important characteristic of theaccelerometer is the level of its intrinsic noise. The ions of iodinewhich act as charge carriers are influenced by gravity and mayaccumulate near the bottom part of the sensing elements 5 when theaccelerometer is mounted. As a consequence, a local change of thesolution density takes place, thus causing free convection. The presenceof free convection inside the sealed housing 1 results in fluctuationand even in self-oscillation of the electric current at the output ofthe accelerometer in the absence of external acceleration. A strictbalance of the content of salt and metallic iodine allows oscillationsto be avoided and minimizes the effect of noise of free convection.FIGS. 14 and 15 present data for different concentrations of thedissolved salts and metallic iodine, where the observation time isapplied on the abscissa and the value of the output current of theclaimed accelerometer in the absence of external acceleration is appliedon the ordinate.

In FIG. 14, the output current is plotted as a function of different KIconcentrations, at a constant iodine concentration of 0.0002 mol/liter.Curves 31-34 correspond to KI concentrations of 4, 3, 2, and 0.2mol/liter, respectively. A comparison of the data given in FIG. 14 showsthat at a fixed concentration of iodine, the amplitude of the outputcurrent due to free convection is acceptable at alkali metal saltconcentration of 2 mol/liter, which practically does not vary even asthe alkali metal salt concentration is decreased.

In FIG. 15 curves 35-38 correspond to the concentration of dissolvedmetallic iodine of 0.8 mol/liter, 0.5 mol/liter, 0.1 mol/liter and 0.02mol/liter, respectively. For these studies, the metallic iodine wasdissolved in a 2 M KI solution. A comparison of the data shows that at afixed alkali metal salt concentration, the amplitude of the outputcurrent due to free convection is a minimum at an iodine concentrationof 0.02 mol/liter. The output current drops monotonically as the iodineconcentration is decreased further.

The convective accelerometer described herein also operates as aninclinometer based on the same principles that are described above,except that the role of the external acceleration is replaced by theangle of inclination of an axis of sensitivity of the accelerometer tothe vector of gravity. It should be noted that the axis of sensitivitydepends on the type of accelerometer involved. For example, forrotational accelerometers having a toroidal channel filled with a liquidagent, as described herein (see e.g., FIG. 1) the axis of sensitivity isperpendicular to the plane defined by the toroidal channel. On the otherhand, the axis of sensitivity of a linear accelerometer having atoroidal channel partially filled with a liquid agent, as describedherein (see e.g., FIG. 24.) has an axis of sensitivity in the planedefined by the toroidal channel. In any event, when the claimedaccelerometer is inclined, the liquid agent 2 starts moving, and theadder 19 produces a voltage proportional to the angle of inclination.

The following description provides some exemplary embodiments of thisinvention.

In one embodiment, two additional electrodes 39, 40 may be installed ata fixed distance from the conductive members 5 as shown in FIG. 10.Generally, the guard electrodes should be as close as possible to theoutermost conductive members of the sensing elements, and may even touchin some embodiments. In other embodiments the outermost conductivemembers of the sensing elements are separated from the guard electrodesby about 5 to about 120 microns. The presence of additional guardelectrodes 39, 40, results in spatial nonuniformity of the concentrationof the charge carriers beyond the conductive members 5, thereby reducingfree convection due to the difference of densities of the liquid agentin the bulk volume and near the surface of the conductive members 5. Forthis application, the shape of the additional guard electrodes 39, 40 isnot particularly limited, and generally may be any shape that (1)provides a large contact area with the liquid agent 2 (i.e., a contactarea that is equal or greater than the area of contact between aconductive member and the liquid agent and (2) has a minimalcontribution to the hydrodynamic impedance (i.e., at least a factor oftwo less than the hydrodynamic impedance of the sensing element). Forexample, the guard electrode may be in the shape of a ring spiral 41,(FIG. 16), a cone-shaped spiral 42 (FIG. 17), or as a flat mesh as shownin FIG. 9. To provide high operational stability, the guard electrodes39, 40 are preferably interconnected by a conductive element 43 as shownin FIG. 18. The guard electrodes 39, 40 (FIG. 10) are connected to thepositive terminal of the power source 20 in preferred embodiments.Furthermore, when more than one installation module is used as describedmore fully below, it is preferable to provide corresponding guardelectrodes for each installation module.

The sealed housing 1 (FIG. 1) is used to house the liquid agent 2 and toprevent any leakage or evaporation of the liquid agent 2. Many types ofmaterials or combinations of materials may be used to fabricate sealedhousing 1, provided that the materials or combination of materialspresent a chemically stable and non-conductive surface to the liquidagent 2. For example, the sealed housing 1 can be made according tostandard ceramic technology using diffusion welding, and also can bemade of quartz, glass or a chemically stable plastic material. Theoutput contacts 8, 9, 10, and 11 are sealed terminals and are used forconnecting the conductive members 5 with an electrical circuit. Incertain embodiments, an upper tank 44, which is made integral with thesealed housing 1, is provided, which serves as an expansion volume tocompensate for the thermal expansion of the liquid agent 2 in a widerange of fluctuation of the environmental temperature. Liquid agent 2 isadmitted into sealed housing 1 through an inlet 45.

The sealed housing 1 (FIG. 19) may be provided with a channel 46 alsofilled with liquid agent 2. The shape of the channel 46 is defined byexternal and internal generating shapes, which may be the same type ofshape or different. The type of generating shape is not particularlylimited and may be any closed shape (e.g., ellipses, circles,rectangles, squares, ovals, or even irregular shapes). For example, whenthe internal and external generating shapes are circular, and thecross-section of the channel is circular, the channel comprises atoroidal duet. It should be noted that this invention also contemplatesnon-toroidal ducts, including those which may have the same or differentinternal and external generating shapes, and/or ducts that do not have acircular cross-section. However, a toroidal duct is advantageous forminimizing the effect of possible housing deformations due totemperature and pressure variations in the external environment, whichcan cause variations in the accelerometer response. Accordingly, anaccelerometer with a toroidal duct has increased sensitivity to motionsof the liquid agent 2 that originate due to forced convection under theeffect of external acceleration even in the presence of environmentalinterferences. The channel 46 contains a liquid agent 2 that istypically admitted through a capillary 47 (FIG. 2), which provides afree flow of the liquid agent 2 from the upper tank 44 into the toroidalchannel 46 (FIG. 19). The toroidal channel 46 can be made in such a waythat the internal and external generating shapes are eccentric withrespect to each other. The degree to which the internal and externalgenerating shapes are eccentric is denoted e, which represents thedistance between the centers of the internal and external generatingshapes. For certain preferred applications, e can vary between about 0.1to about 5 mm. For high frequency applications, it is useful to have aconvective accelerometer with a large value of e (i.e., ≧1 mm, see FIG.19), because the cut-off frequency of the accelerometer increases withincreasing value of e.

Additionally, in some embodiments the frequency range of the convectiveaccelerometer may be varied by varying the value of the hydrodynamicimpedance to the motion of the liquid agent 2 through the use of a“mouthpiece.” Here, a “mouthpiece” is defined as an object that is addedto the sealed housing to increase the hydrodynamic impedance of thechannel 46. For example, a mouthpiece may be installed on one of thewalls of the channel 46 (FIG. 20). The presence of this componentresults in local constriction of the channel 46, thereby increasing thehydrodynamic impedance. The number of mouthpieces 48 may vary and isdetermined by first determining the hydrodynamic impedance required fora particular frequency range, and then determining the number ofmouthpieces that are required to attain that hydrodynamic impedance. Asone of ordinary skill in the art would understand, these parameters canbe determined from routine experimentation. As an alternative to usingmouthpieces, local constrictions in the channel 46 may be achieved bychoosing inner and outer generating shapes that provide the requisiteconstriction of the channel to attain the desired hydrodynamicimpedance. For example, if a toroidal convective accelerometer withcircle of diameter d as the internal generating shape were modified sothat the internal generating shape is a square of side dimension d, thehydrodynamic impedance of the modified accelerometer would be greaterthan that of the original accelerometer. This is because the channelwould be locally constricted at the corners of the square, which wouldextend into the channel.

The conductive member 5 can be arranged in the center of theinstallation module 3 (FIG. 1) at the same distance from each other soas to minimize the difference between the absolute values of thecurrents through each pair of conductive members 100, 200 under thequiescent state and to minimize the deviation of the amplitude-frequencycharacteristics of each pair of conductive members relative to eachother. The conductive members 5 may be located at a fixed distance fromthe walls of the installation module 3 to avoid possible misalignment.When the conductive members are in the form of a mesh (see FIG. 9) thecenters of the holes in the dielectric spacers are preferably oppositeto centers of the cells in the mesh (i.e., spaces between wires).Preferably, the area of the mesh should overlap the area covered by theholes in the spacer with margins equal to the radius of the hole. Toimprove the linearity of the characteristics of the accelerometer, thetoroidal channel 46 (FIG. 19) can be provided with two installationmodules 3 (FIG. 21) located diametrically opposite to each other. Eachof the installation modules 3 includes at least a pair of conductivemembers, but to increase the sensitivity of the accelerometer, theinstallation module 3 may include a second pair of conductive members asshown in FIG. 22. The number of installation modules 3 may be varied,although in some embodiments, it is preferable that an even number ofinstallation modules 3 is used and that the installation modules arearranged symmetrically and evenly spaced about the sealed housing toimprove the linearity of the accelerometer response. (e.g., see FIG.23). In preferred embodiments, the installation modules are arrangedsymmetrically about a toroidal sealed housing to a spatial tolerance of1° or less. In this case, by averaging the data obtained from each pairconductive members, the accuracy of measurements by means of theaccelerometer can be increased considerably, because the measurement'serror decreases with increasing the number of the installation modules nas 1/sqrt(n). Generally, the number of installation modules andconductive members are chosen to achieve an optimum balance between highsensitivity and cut-off frequency.

This invention also provides an accelerometer capable of measuringlinear acceleration. In one embodiment, the linear accelerometercomprises a toroidal duct that is only partially filled with a liquidagent as described herein. As shown in FIG. 24, the toroidal duct forthis type of linear accelerometer is oriented such that the plane of thetoroid is parallel to the direction of gravity g, and at least oneinstallation module 3 containing a sensing element is mounted such thatit is submersed in the liquid agent in the toroidal duct. In a preferredembodiment, the toroidal channel is half-filled with the liquid agent 2.The axis of sensitivity A of this type of linear accelerometer lies inthe plane defined by the toroid and is perpendicular to the direction ofgravity. When the accelerometer experiences an acceleration having acomponent along the axis of sensitivity, the liquid agent flows inresponse to the acceleration, as indicated by the curved arrow in FIG.24, leading to a change in the levels of liquid agent 2 in differentparts of the toroid, as indicated by the dotted lines. This motion ofthe liquid agent is detected by the sensing element in a mannersubstantially similar to that described for the angular accelerometerdescribed above. It will be recognized by one skilled in the art thatnon-toroidal shapes may be used for a linear accelerometer as well. As anon-limiting example, the internal and external generating shapes may beconcentric rectangles or ovals.

The velocity and displacement can also be calculated mathematically byusing the data gathered by the accelerometer, for example, by usingcomputer integration methods well-known in the art. Therefore, thepresent invention can be used as an accelerometer, inclinometer, and ameasuring device for velocity or displacement.

The external dimensions of the accelerometer can be made so small thatthe complete device can be placed in a standard modern 14-pin chip andit can have a configuration of outputs for installation on a standardcard. The device according to the present invention can be made smallenough for various applications including consumer electronics,entertainment devices, control and stabilization systems, sea, groundand air navigation networks, monitoring systems of an automobile anddiagnostic stands, orthopedic devices, neuro-surgical instruments, andintrusion alarm systems. The accelerometer may be mounted horizontally,vertically, or inclined at some arbitrary angle.

With respect to sensitivity, frequency and dynamic range, theaccelerometer exceeds by at least two orders of magnitude all prior artdevices of the same dimensions. A simple design, low production cost,high operational reliability under different conditions make itextremely suitable for mass usage in quite different practicalapplications.

While the invention has been described in detail with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modification can be made, and equivalentsemployed, without departing from the spirit and scope of the invention.

Example 1

This example provides an angular accelerometer having a singleinstallation module. The installation module was installed in a toroidalsealed housing having the following parameters:

1. diameter: 9 mm

2. channel size: 2×2 mm,

3. value of e: zero.

The sensing element contained 4 electrodes that were separated by 3spacers. The electrodes were 30 μm thick metal plates that had an areaof 2×2 mm and nine circular holes with a diameter of 200 μm. The spacerswere 45 μm quartz plates with an area of 2.5×2.5 mm. The spacers alsohad nine circular holes with a diameter of 200 μm.

The transfer function of the accelerometer was measured using arotational oscillating shake-table (IMV, Japan) for the 20-1000 Hzfrequency range and a rotational oscillating calibrator provided forthese tests by Center for Molecular Electronics (CME), Russia for the0.08-40 Hz frequency range.

The IMV shake-table was driven at constant angular acceleration in therange 80-400 rad/s² in the frequency range 20-800 Hz. The tested sensoroutput signals were recorded and analyzed by PCS32i, Velleman digital PCoscilloscope/spectrum analyzer.

The maximum angular displacement of CME calibrator was 1°. This valueconfined the maximum acceleration and consequently the output signal ofthe sensors, especially at low frequencies. As a result, at lowfrequencies the output signal of the sensor could fall below theresolution threshold of the 12-bit digitizer that was used in thecalibration process. Therefore, the calibrator was driven at maximumangular displacements achievable with this equipment. Additionally, thepreamplifier with the factor of 100 for the frequency range 0.08-3 Hzwas used. The calibration data were accumulated and processed using thespecial hardware and software integrated with calibrator setting.

The resultant curve, reduced to the original accelerometer gain is shownin FIG. 25.

The noise tests were performed at night. A 24-bit high-resolutiondigitizer was used to record data for 6 hours. Two identicalaccelerometers were positioned with sensitivity axes aligned in the samedirection, and a correlation data processing technique was used tosubtract the seismic signals and correlated part of digitizer self noisefrom the recorded data. The final noise was calculated by averaging over16 samplings. In this case, the self-noise-floor of the sensors in thefrequency range 0-500 Hz was found to be frequency-independent. Aftersubtraction of the correlated part of the signals (to exclude thedigitizer self-noise) the absolute value of the self-noise floor wasfound to be equal to −85 dB, relative to 1 rad/sec²/√Hz. The integratednoise had the following value:

@ 1 Hz in the pass band 1 Hz−5×10⁻⁵ rad/sec².

The full range of the sensor was greater than or equal to 400 rad/sec².For this range the harmonic distortions and the gain dependence on thesignal level were below the accuracy of the experimental equipment whichwas equal to 4%. Also, the dynamic range, defined as the ratio of thesensor full-range to the noise level has the following value:

138 dB relative to the noise in the passband 1 Hz @ 1 Hz.

Example 2

One of the critically important uses of the claimed convectiveaccelerometer is for improving homeland security. Towards this goal, theaccelerometer may be used in many ways. Three non-limiting examples aredescribed here: intruder detection, intruder identification, and remotelie-detection.

With respect to intruder detection, the high sensitivity of the claimedconvective accelerometer permits remote sensing of the presence of anintruder, even through the walls and floors of a building, by detectingthe intruder's footsteps and/or physiological signals, such as heartbeatand respiration. Such detection is possible even in noisy urbansettings, by using signal processing procedures well known in the art,(e.g. derivative spectra). FIG. 26 shows the signature of a personwalking, as recorded by a rotational accelerometer mounted to the floor.Note that it is possible to distinguish separate steps (marked by thearrows) of the person, even though he was walking on another floor andat a distance of more than 10 meters from the accelerometer. FIG. 27.shows heartbeat and respiration signals of a person recorded by arotational accelerometer positioned about two meters from the person andoperated with a 24-hit digitizer at 40 sps (i.e. 40 samplings persecond). The distance of such remote recording can be increased up to 6meters by increasing the sensor dimensions and decreasing thehydrodynamic impedance of the accelerometer. Remote sensing using theconvective accelerometer described herein has advantages over optical orinfrared-based intruder detection methods, which often require a directline-of-sight between the intruder and the detector.

In addition to intruder detection, the claimed accelerometer may be usedto identify a person on the basis of his physiological signals. Forexample, FIG. 28 illustrates a frequency spectrum (a “physiologicalseismogram”) for heartbeat and respiration signals of a person obtainedby using the rotational accelerometer according to this invention. Asshown in the figure, distinct spectral features have been assigned to aperson's respiration and heartbeat. Because people generally havedifferent heart rates and breathing patterns, the ability to generate anpersonal profile based on such parameters is invaluable for identifyingthe person or distinguishing between two or more people.

This invention also contemplates the use of the accelerometer for remotelie-detection. As is known in the art, certain types of lie detectorsoperate by detecting changes in a person's heart rate caused byincreased nervousness when a person lies. Because the convectiveaccelerometer described herein is capable of detecting a heartbeatremotely, the convective accelerometer can be used as a remotelie-detector. For example, by mounting the convective accelerometer neara ticketing counter in a airport (e.g. under the floor), airlinepersonnel can determine if a potential passenger becomes more nervouswhen asked about the contents of his luggage. Moreover, because thesensing is done remotely and hence surreptitiously, the potentialpassenger, if truly a terrorist, would not know to calm himself down togive a false reading, as he might if he were being strapped to aconventional polygraph. In this way, a more accurate assessment of thepotential passenger's emotional state can be obtained.

Example 3

This example shows that the convective accelerometers according to thisinvention may be adapted for use in seismic applications, such asseismic imaging or oil exploration. In particular, the rotationalaccelerometers as described herein can be adapted to measure thedifferential seismic field, or, more accurately, the curl of thedisplacement field directly. In contrast, prior measurements of thedifferential seismic field were indirect and required two spaced linearsensors and a series of calculations based on the outputs of the linearsensors.

By using a combination of linear and rotational accelerometers asdescribed herein, it is possible to obtain substantially moreinformation on subsurface geological conditions by 3D high-resolutionseismic measurements. Unlike a conventional geophone, which is onlycapable of recording the first arrival of a seismo-acoustical signal,the combination of rotational and linear convective accelerometersseparately capture the both the first arrivals of transverse waves bythe rotational sensor, as well as that of longitudinal waves by thelinear sensor. This is because the rotational sensor is insensitive totranslational motions and the linear sensor is insensitive to rotationalmotions. Thus it becomes possible to measure Δt=t_(l)−t_(t) with highaccuracy, where t_(l) and t_(t) are the moments of the first arrivals oflongitudinal and transverse waves respectively. The separation of thearrivals for longitudinal and transverse waves allows for determiningnot only Young's modulus, but also Poisson's ratio. Therefore, muchhigher accuracy in the identification of the properties of the mediumalong the waves' propagation becomes possible.

Another advantage of the proposed instrument is that the data from thecombination of the rotational and linear accelerometers allowinterpolation between specific installation points to determine theseismic field between these points, thus obtaining a high-resolutionimage of the seismic field for the same or smaller number of measurementpoints, compare with traditional approaches.

The following provides parameters of inexpensive high-resolution 3-Dseismic instrumentation that have been built using the linear androtational accelerometers according to this invention.

-   -   Frequency range: 1-1000 Hz;    -   Dynamic range: 126 dB;    -   Noise level: 5×10⁻⁵ rad/sec²/√Hz for rotational channel        -   and 10⁻⁶ m/sec²/√Hz—for linear channel;    -   Power consumption: 5 mA from 12 Volts;    -   The temperature range: −40° C. to +55° C. (optionally up to        +100° C.);    -   The overall combined sensor system dimensions:        -   diameter: 30 mm        -   length: 170 mm.            The high sensitivity and the small size of the sensors allow            one to essentially simplify measurements and to reduce their            expense, because it makes it possible to decrease the            diameter of the boreholes, to increase the distance between            them, and to reduce the power of the signal source. It            substantially increases the amount of information obtainable            and improves the resolution power of 3-D seismic            measurements.

The convective accelerometers of this invention also opens newopportunity for drilling equipment control during the both oil or gasextraction and/or exploration. Generally, there are two approaches tocontrol drilling equipment during oil or gas extraction: (1) sensors areplaced on the drill. In this case there are several problems with properoperation of the sensors in an environment of high vibration andtemperature, and with transmission of the data to the surface; or (2)sensors are placed on the earth's surface. In this case sensors shouldbe extremely sensitive to detect the signals generated by the drillingequipment and also be capable of selecting useful signals in noisyenvironments.

This example focuses on the second approach, and in particular uses aseismic network equipped with low-noise, high-quality, broadbandconvective accelerometers that can measure drilling equipmentparameters, similar to the measurement of earthquake parameters. Spectraobtained using conventional sensors are shown in FIGS. 29-32. In thesestudies, the sensors were installed on the earth's surface. Data areshown for a low-cost vertical geophone (model CB-10, frequency range5-120 Hz: the Russian analog of the Guralp (UK) model CMG40T), and alinear three-component broadband seismometer (model CME4011, frequencyrange 0.033-20 Hz: the Russian analog of the Mark Products (USA) modelL28). The sensors were placed at a distance of 600 meters from thedrilling rig, while the operating drill was located at an approximatedepth of 1 km under the earth's surface. The experiments were performedduring the spring flood period and the drilling rig and sensors werelocated on two islands, separated by shallow water.

The following conclusions can be drawn from the data presented: (1) thelow-cost vertical geophone (FIG. 29) did not detect the low-frequencysignals produced by the underground equipment and consequently wasuseless for the purpose of the experiment; (2) the broadband seismometerrecorded the peaks, corresponding to the translational motions of thedrilling equipment (peaks at 1.1 Hz in FIGS. 31-32); and (3) none of thelinear accelerometers used in the test detected the spectral componentscorresponding to the drill rotations.

However, drill rotations were measured with a rotational convectiveaccelerometer having a resolution of 5×10⁻⁷ rad/sec and a frequencyrange of 0.05-100 Hz. Its operational principle is illustrated in FIG.33. FIG. 34 presents the image of the three-component rotationalconvective accelerometer, and FIGS. 35-37 show the spectra recorded withthe three-component rotational sensor. Only the rotational sensordetects the frequencies corresponding to the frequency of the drillrotation (0.8 Hz) and its second and third harmonics (1.6 and 2.4 Hz,correspondingly). These peaks disappeared when the drill was stopped andreappeared after renewal of operation. Such peaks could not observed inthe spectra of the linear accelerometer, since they were masked by abackground seismic noise related to water surface oscillations, whichwas especially significant on windy days. This noise, however, did notaffect the rotational sensor, due to the spatial filtration capabilityof the rotational sensor.

The results of this experiment show that rotational sensors have greatpotential in the oil and gas industry in the following areas: (1) remotemonitoring of the drill condition; (2) determining the drillingdirection, made possible by using the relationship between the amplitudeof the signals measured by all three components of the rotationalsensor; (3) determining the position and velocity of the drill, by usingthe instant direction of the drill and the drilled-in distance. Itshould be emphasized that all these measurements and the data processingcan be performed from the earth's surface to a distance of up to ˜1 kmfrom the drilling rig.

1. A convective accelerometer comprising: a sealed housing; a liquidagent comprising an electrolyte solution, wherein said liquid agent iscontained in said sealed housing; an installation module secured in saidsealed housing; a sensing element that is sensitive to convection,wherein said sensing element is fixed in said installation module andimmersed in said liquid agent, such that the liquid agent flows throughsaid sensing element under conditions of forced convection caused by anacceleration applied to the convective accelerometer, and an electriccircuit connected to said sensing element, wherein said electric circuitamplifies and processes the output signals generated by said sensingelement.